In the drilling of oil and gas wells as well as other downhole activities, it is common to use a downhole system which provides a percussive or hammer effect to the drill string to increase drilling rate. For example, in the process of drilling a wellbore, frictional forces acting against the drill pipe or other component running through the wellbore limit the maximum length or depth to which the wellbore may be drilled. Solutions of this problem include mechanisms for vibrating the drill pipe during drilling in order to convert static frictional forces on the drill pipe to dynamic frictional forces between the drill pipe and the wall of the wellbore.
Various types of vibrator devices have been employed with pipe strings in order to provide vibration. Some such vibrator devices typically employ reciprocating impact elements that move back and forth along the axis of the pipe string to induce vibration in the pipe string. Other such vibrator devices employ the use of eccentrically weighted rotating masses, eccentric shafts or rods, or rotatable impact elements that rotate about the longitudinal axis of the drill or pipe string to strike an impact anvil in order to apply a rotational or torsional vibration to the pipe string.
Still other types of vibrator devices utilize Moineau power sections that are generally used in downhole mud motors or pumps. Moineau power sections typically utilize rubber or rubber-like elastomers as seals which are negatively affected by elevated wellbore temperatures and pressures, certain drilling fluids and or chemicals, and contaminants or debris in the wellbore or drilling fluids.
Apparatus utilizing one or both of these principles is described in U.S. Pat. No. 5,165,438 to David M. Facteau. Two fluidic oscillators are achieved by employing wedge-shaped splitters to route the flow of a fluid down diverging diffuser legs. The oscillators connect to a source of fluid flow, provide a mechanism for oscillating the fluid flow between two different locations within the oscillator, and emit fluid pulses downstream of the source of the fluid flow. In one vibrator, a feedback passageway from each leg is routed back to the flow path upstream of the splitter to create a condition establishing oscillating flow through the legs. In a second vibrator, a passageway between the legs downstream of the upstream end of the splitter creates a condition establishing oscillating flow through the legs. A disadvantage of this kind of oscillator is that the diverging diffuser legs required to establish oscillation are expensive to fabricate and prone to clogging from debris in the fluid because of the relative incline between the leg and the axial of the pipe string.
Consequently, there is a need to provide an even more effective fluid oscillator for down hole tools which is reliable, long-lived and economical.